Rotating equipment is sometimes used in hazardous environments, such as a downhole environment in oil and gas wells, which is very hostile to equipment. The downhole pressures and temperatures are usually higher than the ambient conditions. The downhole fluids can contain very corrosive species like H2S and CO2. In addition, there can be sand, debris, and other solids in the wellbore. The usable life of the equipment exposed to the downhole environment is often much shorter due to different failure modes caused by combining these conditions in different ways. High temperature, high strength, and corrosion-resistant materials are used to extend the life of downhole equipment in many cases. However, the presence of debris and solids can still be detrimental to downhole rotary devices at the physical contact points, for example bearing surfaces. Therefore, it is a common practice to protect the contact surfaces of the downhole rotary devices by isolating the downhole environment.
Rotary devices have a shaft to transmit torque. The traditional approach to transmit torque is to use a solid shaft with shaft seals around it to isolate downhole fluids from the motor, bearings, and other parts which need to be protected from downhole fluids and solids. Seals eventually fail, especially under the pressure, temperature, and corrosive downhole environments. Failure of seals leads to the ingress and exposure to downhole fluids for parts that cannot tolerate the downhole fluids. This eventually causes different failure modes of downhole rotating devices. To fundamentally eliminate all these failure modes, the shaft seal can be eliminated. To do so, a magnetic coupling can be used to transmit torques without a solid or mechanically linked shaft, instead using a magnetic field to transmit torque. When there are no shaft seals, there are no shaft seal failures.